Renal cell carcinoma (RCC) is distinguished amongst solid tumors for its resistance to conventional chemo- and radiotherapy but its susceptibility, in a minority of patients, to immunologic manipulation. Regression of metastatic disease is seen in 10-20% of patients who are treated with the immune-modulating cytokines Interleukin-2 and/or Interferon-alpha, and pilot studies have demonstrated that adoptive cellular therapy with ex vivo-expanded autologous lymphocytes can increase the response rate. More recently, regression of metastatic RCC has also been seen in up to 40% of patients who undergo nonmyeloablative allogeneic hematopoietic cell transplantation (HCT) from donors who are matched at the major histocompatibility complex (MHC). Responses in this setting are typically seen several months or more after HCT, after the establishment of complete donor T cell engraftment, and are closely associated with development of graft-versus-host disease (GVHD). This has suggested that tumor regression may in part be attributable to a graft-versus-tumor (GVT) effect mediated by donor cells reacting with minor histocompatibility (H) antigens expressed on recipient tumor cells. Preliminary data presented in this application demonstrate that T cell clones specific for recipient minor H antigens that are expressed on RCC tumor cells can be isolated from RCC patients experiencing tumor regression after nonmyeloablative allogeneic HCT. Identification of the genes encoding minor H antigens expressed on RCC cells and evaluation of their expression in normal and malignant tissues will facilitate the development of therapeutic strategies for augmenting GVT activity after allogeneic HCT. In this proposal, we will isolate CD8+ and CD4+ RCC-reactive minor H antigen-specific T cell clones from RCC patients after allogeneic HCT and use cellular and molecular methods to identify the genes encoding class I MHC-restricted minor H antigens expressed by RCC cells. The specific aims are: (1) Isolate and characterize CD8+ and CD4+ minor H antigen-specific and tumor-specific T cell clones from RCC patients after nonmyeloablative MHC-identical HCT. (2) Identify clonally expanded T cells that are associated with tumor regression in patients with metastatic RCC following nonmyeloablative MHC-identical HCT. (3) Identify the genes encoding antigens recognized by RCC-reactive CD8+ T cell clones isolated from patients with metastatic RCC who exhibit tumor regression after nonmyeloablative HCT.